As is well known, miniaturized acoustic transducers, such as microphones for hearing aids, typically include a device commonly referred to as a motor, comprising a diaphragm positioned in spaced relation with a charged plate. Various structures have been proposed for maintaining the diaphragm in spaced relation with the charged plate.
One such structure is illustrated in Carlson, et. al., U.S. Pat. No. 4,730,283, which is assigned to the assignee of the present invention. According to this structure, a plurality of bumps are provided on the lower surface of the charged plate, radially inward of the periphery of the charged plate, to maintain the diaphragm in spaced relation with the charged plate. While this structure has operated satisfactorily, the bumps affect the resonant frequency of the diaphragm. Additionally, the bumps affect the capacitance and the sensitivity of the microphone. Although the motor is capacitive, this additional capacitance is parasitic in nature and affects the magnitude of the signal which can be transferred to the microphone amplifier.
The present invention is provided to solve these and other problems.